Tuesday, December 13, 2016

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Postmortem of Last Week's Storm

There's an old saying, 'When it rains, it pours.' An atmospheric river #blessed us with copious amounts of moisture, but due to the warmer air associated with the deep moisture plume and lack of a deep trough, we had high snow levels. As fellow Powdictioner Hatchett says 'the sub-tropics giveth, the sub-tropics taketh'.

The good news: we got a lot of rain to continue easing the drought and a lot of snow above 7500-8000 ft.

The bad news: The snow levels mostly above 7000 ft. and for the majority of the heaviest precipitation, the snow levels were around 8000 ft. We received some rain on snow, which as you know, is not ideal for #buildingthebase.

Our friends at the NWS Reno office put together some nice summary graphics (as they always do; much love to our meteorologist brethren) detailing rainfall and snow reports.

Blue Canyon received its 11th largest single day precipitation total and South Lake Tahoe received its 5th largest single day precipitation total. For South Lake, two of its top five single day precipitation records have occurred this fall (10-16 and 12-10). And I always love seeing these stats about the total amount of water that falls and makes it way into Tahoe. The numbers are so large it's really surreal.

With all of that rain, we had some flooding, and the stream flows increased dramatically especially for the Yuba and Truckee Rivers. Below is the hydrograph for the Truckee River in Reno.

We've had a great start to the Water Year for precipitation, and that is mostly due to the strong atmospheric rivers that affected the Sierra in October and last weekend. However, the atmospheric rivers are a double-edged sword, especially when they don't coincide with a deep trough with arctic air. Without the cold air, the relatively warmer and moist sub tropical air bumps snow levels up, but we still get a lot of precipitation, just not as much of the frozen variety as we like.

In fact, we've had such a great start to the Water Year, we are ahead of the record setting 1982-83 Water Year pace. However, that doesn't guarantee that we will stay on that pace. The faucet can turn off, as we've seen all too often in recent winters.

The graphic below, from a dear friend of the Powdiction team and climatologist at the Western Regional Climate Center, shows there is no correlation between October precipitation and November-March precipitation.


So let's celebrate the continued amelioration of the drought in northern California and in most of the Sierra, but it's still ok to be bummed about the lack of snow that has come with it. However, we do have a storm coming Thursday and Friday.

This storm is an INSIDE SLIDER. I love these storms because it can reverse the rain-shadow effect and because of the crazy upslope flow regimes on the east side. And this storm has cold air and a good subtropical moisture source with it. We can expect 6-18" around Tahoe/Donner, but 2-4 feet is possible from Carson Pass down into the southern Sierra.

So expect a Sergio Romo inside slider, but not the ones he was throwing to the Cubs in the NLDS (SPOILER ALERT: I'M A CUBS FAN). We will have more info on this storm tomorrow in another post.

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